I. Field of the Invention
The present invention generally relates to new regulatory sequences with defined tissue specificity. More specifically, the invention relates to the discovery of gene promoters for tissue specific and inducible expression of transgenes for the improvement of plant species.
II. Description of Related Art
Molecular improvement of crops presents both new challenges and clear opportunities for the application of biotechnology. Genetic modification of traits should enhance economics, human and animal health, and the environment. Such modifications require the efficient expression of transgenes with appropriate expression patterns. Regulatory elements with the appropriate expression profile are thus needed.
Most previous studies have used available strong constitutive promoters, such as the cauliflower mosaic virus 35S (CaMV35S) promoter. However, some constitutive promoters do not work in certain plants and typically do not provide tissue-specific or inducible expression in most environments. There has been a general lack of appropriate regulatory elements for inducible and tissue-specific expression in particular.
The ability to express transgenes in an inducible and/or tissue-specific manner is significant because it allows targeted expression to relevant plant tissue(s) under conditions in which transgene expression will benefit the plant. Expression of transgenes in plant tissues in which expression would not benefit the plant may have a deleterious effect on the plant or decrease available energy for expression of other proteins in the relevant tissues, depending upon the transgene expressed. Government regulatory issues may also be simplified by limiting gene expression primarily to inedible plant portions.
One plant characteristic for which genetic modification could greatly benefit the environment and farmers alike is increased phosphorous utilization from soil. Phosphorus is a major mineral nutrient that frequently limits crop production. The form of phosphorus most readily accessed by plants is phosphate (Pi), which is relatively immobile in the soil and often unavailable for plant uptake (Schachtman et al., 1998). Pi levels in soil are occasionally as high as 10 μM, but more frequently as low as 1 μM. In contrast, Pi concentration in plant cells is much higher, in the 2-20 mM range (Vance et al., 2003).
The identification of strong phosphate deficit-inducible promoters in particular could provide a significant advance in the art by allowing improvements for phosphate utilization under only appropriate conditions. Natural phosphorous sources are subject to depletion, while low levels of phosphorous can significantly deplete agricultural productivity and applications of phosphorous-rich fertilizers create run off polluting water sources. The identification of unique regulatory elements capable of use for engineering phosphorous uptake or other traits would therefore represent a significant benefit to agriculture and the environment alike.